Binary, ternary, and quaternary metal chalcogenides have been using as phase change and photovoltaic materials.
Phase-change materials exist in a crystalline state or an amorphous state according to temperature. A phase-change material has a more ordered atomic arrangement and a lower electrical resistance in a crystalline state than in an amorphous state. A phase-change material can be reversibly transformed from the crystalline state to the amorphous state based on an operating temperature. Such characteristics, that is, reversible phase change and different resistances of different states, are applied to newly proposed electronic devices, a new type of nonvolatile memory devices, phase-change random access memory (PRAM) devices. The electrical resistance of a PRAM may vary based on a state (e.g., crystalline, amorphous, etc.) of a phase-change material included therein.
Among various types of phase-change materials used for memory devices, the most commonly used are ternary chalcogenides of group 14 and group 15 elements, such as germanium-antimony-tellurium compounds, commonly abbreviated as GST. Importantly, a phase-change material with a composition of Ge2Sb2Te5 is proven to be the best candidate. The solid phases of GST can rapidly change from crystalline state to amorphous state or vise versa upon heating and cooling cycles. The amorphous GST has relatively higher electrical resistance while the crystalline GST has relatively lower electrical resistance.
Previous arts include the manufacturing of bulk metal chalcogenide phase change materials with metallurgical methods and thin film materials with Physical Vapor Deposition (PVD), chemical vapor deposition (CVD) or atomic layer deposition (ALD) processes. Examples of works in the field are listed below.
Berger, H.; Goetze, U. discloses the preparation of disilyltellurides; Inorg. Nucl. Chem. Lett. 1967, 3, 549-552. Detty, Michael R.; Seidler, Mark D., discloses the synthesis of bis(trialkylsilyl) chalcogenides; Journal of Organic Chemistry (1982), 47(7), 1354-6. Dickson, R. S., Heazle, K. D., discloses the assessment of some Sb—Te single-source compounds for MOCVD applications; J. Organometal. Chem., 493 (1995) 189-197. Choi, B. J., et al, discloses the deposition of Ge2Sb2Te5 films in cyclic PECVD process using metallorganic precursors; J. Electrochemical Soc., 154 H318-H324 (2007). Jung-Hyun Lee et al, discloses the making of GST films from aminogermanes, aminostilbines, and dialkyltellurium; US 2006 0172083 A1; discloses the tellurium precursors for GST films; US 2006 0180811; and discloses the antimony precursor for GST films; US 2006 0049447. Duncan W. Rown et al, discloses the use of organometallic tellurium compounds using fluorinated alkyl tellurium compounds in CVD process; U.S. Pat. No. 5,312,983. Moungi G. Bawendi et al, discloses the tellurium-containing nanocrystalline materials produced by injection of a precursor into a hot coordinating solvent, followed by controlled growth and annealing; U.S. Pat. No. 7,060,243 B2.
One of the technical hurdles in designing PRAM cell is that in order to overcome the heat dissipation during the switching of GST materials from crystalline to amorphous states a high level of reset current has to be applied. This heat dissipation, however, can be greatly reduced by confining GST material into contact plugs, thus reducing the reset current needed for the action. Since the GST contact plugs are of high aspect ratio structure, conventional sputtering process for GST film deposition can not achieve high comformality. This drives the need for precursors and related manufacturing methods or processes for forming GST films by chemical vapor deposition (CVD) or atomic layer deposition (ALD) processes, which can produce films with high conformality and chemical composition uniformity.
Similarly, the needs arises from the thin film making of a photovoltaic (PV) materials for the application such as the solar cell. A photovoltaic (PV) device absorbs light and generates electricity. The absorption of light and separation of charges happen in the active materials in a PV device. Development of efficient and low cost photovoltaic devices is key to significant utility of direct solar energy to electrical power conversion. Crystalline silicon is among the best-known semiconductors for photovoltaic devices and is widely employed. Other useful materials are thin films of amorphous silicon (a-Si), Copper Indium Selenide (CIS), Copper Gallium Delenide (CGS), Polycrystalline Copper Indium Gallium Selenide (CIGS), Cadmium telluride (CdTe), and organic material. The elements useful are cadmium, tellurium, indium, gallium, selenium, germanium and ruthenium.